This original collection revisits and re-evaluates Chomsky's classic competence/performance distinction from a wide variety of perspectives and areas of expertise. The discussion is placed within a broad framework, taking account of a view of language both as a societal construct and as internal, developing within the mind and/or brain. Renowned experts in the fields of lexis, sociolinguistics, connectionism, Universal Grammar, language testing and interlanguage draw together ideas from the most recent developments in second language learning and psychological theory. Germane to their debate is the question of whether it is helpful, or in principle possible, to draw a distinction between competence and performance in second language learning.